The high surface and internal areas of activated carbon have made it useful in many separative, adsorptive, and purification processes. Preparation of improved carbonaceous adsorbents by pyrolysis of synthetic resins, such as crosslinked polystyrene, or of polymers treated with oxidants to increase the yield of carbonaceous product, has been known for some years. Useful adsorbents from partially pyrolyzed porous precursors, especially those based on crosslinked, stabilized (treated with fixatives or oxidants to prevent depolymerization) polyvinyl aromatics, represent an improved version of such materials. Neely, U.S. Pat. No. 4,040,990, which is hereby incorporated into the present specification by reference, and in Carbon, 19, 27 (1981), describes controlled partial pyrolysis of macroporous monosulfonated (or otherwise fixated) polystyrene to produce charred beads maintaining the macroporous structure of the precursor polymer but with microporosity created during heat treatment. Neely further teaches adsorptive and purification uses for such pyrolyzed polymers; see also U.S. Pat. Nos. 4,063,912 and No. 4,267,055. The term "carbonaceous adsorbent" as used herein refers to particles prepared by the process of Neely from sulfonated macroporous polystyrene resins.
During the many years of research on polystyrene-based cation exchange resins based on the introduction of sulfonic acid by sulfonation with sulfuric acid or chlorosulfonic acid, methods have been found to increase the resin capacity by introduction of more than one sulfonic acid per aromatic ring. Methods for polysulfonation are taught, inter alia, by Corte et al., U.S. Pat. No. 3,158,583, for conventional, non-macroporous resins.
There is little specific information in the art as to preparation of polysulfonated macroporous resins, although such have been marketed and described in the trade literature. U.S. Pat. No. 4,224,415 claims a process for sulfonating macroporcus polymers with a sulfonating agent selected from the group of concentrated sulfuric acid, oleum, sulfur trioxide, and chlorosulfonic acid. It fails to teach that polysulfonated resins result from such a sulfonation, nor does it teach any advantages for the resulting resins.
British Patent No 1,525,420, in a broad description of method for rendering infusible various porous high molecular weight compounds (including macroporous resins), and then calcining them, relates techniques for polysulfonation earlier described by Corte et al. among those suitable for creating infusibility. No characterization data are given for the polymer prior to calcination. Preferred infusibility reactants are sulfur trioxide, sulfuric acid, or chlorosulfonic acid. This reference discloses pyrolysis of macroporous resins treated with 15% fuming sulfuric acid and pyrolyzed, and describes an experimental method for determining the porosity of the pyrolyzed material down to 2-5 nm. The results described in the tables of the reference show the absence of any porosity development below 5 nm, and multimodal porosity is not taught. In contrast, Neely in the cited references fully shows the development of microporosity for monosulfonated macroporous resins. Further, the British patent is silent about the processing advantages observed in pyrolysis of polysulfonated resins.
Japanese Kokai 52-30800, filed at the same time and by the same applicant as British 1,525,420, teaches broadly and with very limited exemplification several methods for making macroporous resins and a large variety of methods for making the porous polymer infusible, including but not distinguishing sulfuric acid, sulfuric acid anhydride, sulfur dioxide, and chlorosulfonic acid. A polystyrene in which micropores are produced by extraction of a water-soluble polymer is exemplified as being treated with fuming 15% sulfuric acid at 80.degree. C. for an unknown time and pyrolyzed, but the data show no micropore development below 15 nm.
Japanese Kokai 53-50088, to the same applicant as British 1,525,420 and Kokai 52-30800, teaches preparation of improved adsorbents by pyrolyzing infusible resins made from monomer mixtures containing multiple, non-conjugated, ethylenically unsaturated groups by suspension polymerization in the presence of a precipitant liquid that is a solvent for the monomers and does not swell the polymer. The porous resin so produced is made infusible by a process such as sulfonation or nitration and then pyrolyzed. It is stated that the method can be used to produce pore volumes of 0.1 cc/g., preferably 0.3 cc/g and pore sizes of 1 to 5000 nm, preferably 5 to 1000 nm. The single experiment reported teaches preparation of a non-macroporous (gellular) styrene/divinylbenzene copolymer, sulfonation for six hours at 110.degree. C. with 15% fuming sulfuric acid, and pyrolysis at a temperature of 1000.degree. C., achieved by heating under nitrogen gas at a rate of 300.degree. C./hour. The resulting resin was reported to have an average pore diameter of 20 nm and 0.6 cc/g of pores with diameters of 5 nm or more, with no mention of smaller pore sizes or of macropores. Activation of the pyrolyzed resin with steam at 800.degree. C. to yield a resin with a surface area of 1100 m.sup.2 /g. is noted. There is no direct demonstration in the patent that pore sizes and adsorptive behavior of the present invention can be achieved, as there is no exemplification of polysulfonation conditions being preferred, or of such being applied to a macroporous resin.
In Japanese Kakai 62-197308 is taught a method for producing a porous carbon material having a large void fraction by pyrolysis of a synthetic, crosslinked, styrene-divinylbenzene polymer which has been wetted with concentrated sulfuric acid under reduced pressure and then carbonized in an inactive gas stream.
In Japanese Patent Application 62-76093, filed Mar. 31, 1987, is taught the use of commercially available macroporous resins from Rohm and Haas Co. prepared by the method of Neely for the removal of pyrogens from water. The examples are merely duplicates of those examples presented in British Patent 1,525,420 discussed above and shown not to produce a microporous structure, except that the newer application further discloses further activation by steam for two hours at 800.degree. C., with results exactly those disclosed in Japanese Kokai 53-50088.